1. Field of the Invention
The present invention relates to a device for controlling the flow of liquid metal, particularly a tundish for directing liquid metal from a ladle to a plurality of molds in a continuous casting process.
2. Description of the Related Art
When liquid metal is poured from a ladle normally containing only a single outlet into a multiple number of molds, an intermediate vessel called a tundish is required to distribute the metal between these molds. Practical considerations, such as, ease of installation and repair of the refractory lining of the tundish to the relationship of the tundish to the molds and secondary cooling apparatus, indicate the requirement for a simple tundish shape which can supply metal at a nearly constant rate to molds which are arranged along a single axis.
In the prior art, a very simple tundish consisting of either a trough or box shaped vessel having a generally horizontal or flat bottom with walls is commonly used. In these designs, the stream pouring from the ladle enters the tundish in a position adjacent to one or more of the tundish nozzle outlets, generally on or close to the axis which adjoins the tundish nozzle centers. The problems encountered with these tundish arrangements include:
1. Thermal nonhomogeneity in the liquid metal contained in the tundish. This results in tundish exit streams having different temperatures with the colder metal exiting the nozzle furthest from the ladle stream and hotter metal exiting from the streams closest to the ladle stream.
2. Short-circuit flow and different liquid metal residence time distributions associated with each tundish to mold stream.
3. Turbulence within the tundish caused by the dissipation of the kinetic energy in the ladle streams. The turbulence is propagated above adjacent tundish nozzles and disturbs the smooth flow which is required to properly fill the molds.
4. This turbulence and the pattern of liquid metal flow within the tundish does not allow the separation by floatation of buoyant slag and inclusion particles entrained within the liquid metal.
5. The pattern of flow generated within the tundish can include stagnant or dead flow regions indicating that the input energy from the incoming ladle stream is not properly distributed.
More complex tundish geometries have been used with the objective of allowing the ladle stream entry position to be displaced away from the axis joining the tundish exit-nozzle centers in order to alleviate some of the above problems. These include T-shape and Delta-shape tundish designs. These designs are partially effective at reducing the problems associated with turbulence by moving the turbulent region further away from the exit nozzle positions. However, this can exacerbate problems associated with stagnant regions, thermal homogeneity, short-circuit flow patterns, liquid residence distribution, refractory life and repair, and inclusion removal.
Other prior art tundishes are disclosed in U.S. Patents Nos. 4,711,429, 4,671,499, 4,653,733, 4,177,855 and 4,042,229. Some of these have only been used for limited purposes, such as for mixing alloys with different specific gravities. None of the tundishes can solve all of the problems of stagnant regions, thermal non-homogeneity, short-circuit flow patterns, liquid residence distribution, refractory life and repair and inclusion removal.